As for the stem, there may be some kind of notched piece that has to slide out before you can move it. This is what I've observed of a couple adjustable stems that I've dealt with. The design is such that the screw can come loose a bit without the stem suddenly flopping around. I'd avoid the hammer until I was utterly certain of how it works.
Looks like a fun bike. I suspect that all bikes need some TLC when they arrive from the factory.